For me it was both the practice content, the focus on how I practiced it and the mindset I had when practicing it.
I always practice in the context of an actual song and practice Incrementally in dificulty and not moving on until i could play the current practice material through the song to tempo at least 3 times without mistakes.
For example:
- I'd take a tune I really liked and memorise the chord changes (roots only)
- Then play purely the triads through the changes staying in one position on the fretboard only (note - not with the chords written in front of me but from memory / ear)
- Similar exercise but staying in one direction on the fretboard so if I was on the first position and the first chord was Am7 and the second chord was D7 (one bar each) I would play G, A, C , E and then carry on with the direction of travel but changing chord the next note would be F# A C and back down to the A again. (I have no idea if this makes sense but it' an amazing exercise to change chords without changing the direction of your line)
- I'd then experiment with adding chromatics in to the basic chord tones and see if I can start to 'Hear' which chord tone I'm aiming for
Other things I've practiced would be learning a whole solo by somebody I love to listen to and pick it a part to see If can integrate some of the licks into my own playing for various chord types.
I think the biggest thing I learned was in my mindset to practicing - Focus on the work and not on the results. The results will come naturally as part of the work. But if you focus only on the results I guarantee you'll become frustrated and likely give up.
I also limited myself to only sticking to one or two things when practicing otherwise I just practiced 10 things really badly.
Only my very humble experiences and I am by no means an expert! Hope at least some of that helps you my friend.